In the treatment of heart disease it is often desirable to measure the "global" blood flow rate, which is the measure of the entire flow of blood through the coronary artery where it joins with the aorta. In the prior art such blood flow, as well as selective coronary blood flows in branches of the coronary artery, may be measured typically with a Doppler-type blood flow measuring catheter which carries a Doppler measuring crystal in its tip, which crystal is electrically connected by a wire extending through the catheter from the distal tip to electronics located beyond the proximal end of the catheter.
Signals are emitted from the Doppler crystal at the distal end of the catheter, which signals bounce off of moving blood cells and are sensed. Through the Doppler effect, the velocity of the blood cells relative to the Doppler crystal can be determined, and from that the blood flow rate present in the vessel being measured is determined.
Medical probes which make use of such Doppler measuring means are at the present time commercially available. Such probes may be sheathed wire probes without a lumen, or catheters with a lumen to permit the flow of fluids to and from the site where the blood flow velocity is being measured.
Example, the Millar MIKRO-TIP brand Doppler system is commercially available, being typically a probe without a lumen having a Doppler chip velocity sensor adjacent its distal end. Also, the NuVEL brand Doppler diagnostic catheter is manufactured and sold by NuMed Inc. of Hopkinton, N.Y. Also, a Doppler flow measuring catheter is sold by the Cordis Corporation of Miami, Fla.
Other literature relating to Doppler blood flow velocity catheters exists as well. For example, the publication by Morton J. Kern, M.D. entitled Intracoronary Doppler Blood Flow Velocity Catheters is pertinent for a discussion of the background and use of such catheters.
When selective coronary flow is measured in a particular branch of the coronary artery system, a relatively narrow catheter or probe is used, which probe measures a much lower blood flow volume than in the case of the measurement of global flow at the junction of the coronary artery with the aorta. When one attempts to measure global flow in the enlarged junction of the coronary artery with a catheter which is narrow enough to measure selective coronary flow in branch arteries, for example using a NuVEL type guidewire device, disadvantages are found. This results at least in part from the fact that the flow through the trunk portion of the coronary artery is faster in the center than it is near the edges, in accordance with conventional fluid dynamics. When one attempts to measure blood flow velocity with a thin guidewire type Doppler device, the device may move laterally around inside the large coronary artery trunk, recording different flow rates when it is at a central portion in the artery than when it is adjacent the artery wall. Thus an inaccurate reading can result.
Accordingly, it is generally desirable to use a larger diameter catheter-type device for reading global coronary flow reserve. With the use of a soft, larger diameter catheter type structure, one can use the "pull back method" to pull the catheter up against the wall of the coronary trunk to stabilize it, to obtain a constant, reproducible global coronary artery flow reading.
However, it has been found that such catheters for reading global arterial flow, and which are of cylindrical cross section adjacent the distal tip, exhibit the disadvantage that the cylindrical cross section of the tip can tend to block flow to the coronary tree. In response to this, experimental efforts were made by others to place flow grooves in the periphery of the Doppler measuring catheter, without great success in remedying the flow obstruction problem. At the same time, a simple reduction of diameter of the catheter may not be feasible because of the need to incorporate near the tip a Doppler crystal and an injection lumen, and also for the reasons discussed above.
In accordance with this invention, a medical probe, typically a catheter, is provided in which a Doppler crystal can be accommodated, and also a lumen if desired, while at the same time adequate flow can be provided in the trunk of the coronary tree for adequate measurement of global blood flow through velocity measurement.